Electric Compressor Having Drive Circuit Integrated Thereinto

ABSTRACT

Disclosed is a drive circuit-integrated electric compressor, which is adapted to cool a power semiconductor element in a motor drive circuit with good efficiency without increasing the temperature of sucked refrigerant gas and while suppressing increase in pressure loss in a path for cooling. Specifically disclosed is a drive circuit-integrated electric compressor into which a motor drive circuit having a power semiconductor element is incorporated integrally, characterized in that the electric compressor is configured so that the power semiconductor element in the drive circuit is cooled by refrigerant gas to be discharged.

TECHNICAL FIELD OF THE INVENTION

This invention relates to a drive circuit-integrated electric compressorwhich has a built-in motor and into which a motor drive circuit fordriving the motor is incorporated integrally, and specifically, relatesto a drive circuit-integrated electric compressor which is adapted tocool a power semiconductor element mounted on the motor drive circuitefficiently.

BACKGROUND ART OF THE INVENTION

In Patent Document 1, disclosed is a scroll-type electric compressorwhich has a built-in motor for driving a compression mechanism part andinto which a motor drive circuit for driving the motor is incorporatedintegrally. In this motor drive circuit, particularly into its inverter,a power semiconductor element is assembled, and because the powersemiconductor element generates heat, it is generally preferred to coolthe element in order to secure the normal operation. Semiconductorscurrently used, including power semiconductor elements, usually consistof silicon (Si). Because the upper limit of the operating temperature ofsuch a conventional power semiconductor element is about 150° C., it ispreferred to cool the element so as not to exceed the upper limit. InPatent Document 1, utilizing refrigerant being sucked into a compressor,this cooling is carried out.

Prior Art Documents Patent Documents

Patent document 1: JP-A-2000-291557

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

However, in the method for cooling the power semiconductor element in amotor drive circuit utilizing the sucked refrigerant gas as describedabove, there is a fear that following problems may occur. Namely,because sucked refrigerant gas may be overheated by heat of the powersemiconductor element, there is a fear that compression efficiency ofthe compressor may be reduced. Further, because a temperature of acompressed gas also elevates when the sucked gas is overheated, there isa possibility that a problem of thermal resistance on each part in thecompressor may occur, thereby causing a fear that the life of thecompressor may be shortened. Furthermore, because the sucked gas passesthrough a heat exchange route formed for cooling the power semiconductorelement, there is a fear that the pressure loss in a refrigerant path inthe compressor may increase and the compression efficiency may also bereduced.

Paying attention to the problems with the method for cooling the powersemiconductor element in the motor drive circuit using suckedrefrigerant gas as described above, the object of the present inventionis to provide a drive circuit-integrated electric compressor which canefficiently cool the power semiconductor element in the motor drivecircuit, basically without elevating the temperature of suckedrefrigerant gas and while suppressing the increase of pressure loss inthe path for cooling.

Means for Solving the Problems

To achieve the above-described object, a drive circuit-integratedelectric compressor according to the present invention is an electriccompressor into which a motor drive circuit having a power semiconductorelement is incorporated integrally, characterized in that the electriccompressor is configured so that the power semiconductor element of thedrive circuit is cooled by refrigerant gas to be discharged. Namely, itis not configured so as to be cooled by sucked refrigerant gas as in theconventional technology, but it is configured so as to cool the powersemiconductor element utilizing refrigerant gas to be discharged afterhaving passed through a compression mechanism part of the compressor.

Namely, because the refrigerant gas to be discharged is used for coolingthe power semiconductor element, the problems caused in case of usingsucked refrigerant gas, that is, a decrease in compression efficiencycaused by a temperature elevation of the sucked refrigerant gas, adecrease in life of the compressor caused by a temperature elevation ofa compressed gas, an increase in pressure loss caused by passing of thesucked refrigerant gas through a heat exchange route for cooling and adecrease in compression efficiency accompanied with the pressure loss,do not occur basically. In other words, because sucked refrigerant gasis not used for cooling, the gas temperature does not elevate as in theconventional structure until the sucked refrigerant gas is compressedand discharged, and therefore, it is possible to secure a highcompression efficiency and to contribute to improve the coefficient ofperformance (COP) of the compressor. Further, in a refrigerant path inthe compressor, since the elevation of the gas temperature is suppresseduntil sucked refrigerant gas is compressed and discharged, thedurability of the compressor is improved and the life thereof islengthened. Moreover, because sucked refrigerant gas does not need topass through the heat exchange route for cooling as in the conventionalstructure, the pressure loss in the refrigerant path in the compressoris reduced. Furthermore, in case of a configuration that a neodymiummagnet is used for a rotor as a compressor built-in motor, the magnetmay be demagnetized because of the elevation of the temperature. In theconventional case where the power semiconductor element is cooled bysucked refrigerant gas, there has been a fear that the magnet may bedemagnetized because the gas passes through the motor after thetemperature of sucked refrigerant gas has been elevated by heatexchange, whereas in the present invention, such a problem can be solvedbecause cooling is performed by refrigerant gas to be discharged whichhas passed through the motor.

In the present invention, however, because refrigerant gas to bedischarged which has a higher temperature than that of suckedrefrigerant gas is used for cooling the power semiconductor element, thepower semiconductor element may be cooled to a higher temperaturerelative to that of the conventional structure. Therefore, it isnecessary to use a semiconductor element having a higher thermalresistance, that is, a higher operating temperature limit, as the powersemiconductor element.

In order to satisfy this necessity, in the present invention, a wideband gap semiconductor element can be used as the above-described powersemiconductor element. Namely, as aforementioned, all the semiconductorscurrently used, including power semiconductors, consist of silicon (Si).Recently, a wide band gap (WBG) power semiconductor is being developedas a semiconductor material to be replaced from silicon. Because theupper limit of the operating temperature of the WBG semiconductor is200° C. or higher whereas that of the conventional Si powersemiconductor is about 150° C., it becomes possible to cool itsufficiently down to a desired temperature even by the refrigerant gasto be discharged with a temperature which is generally in a range of100-150° C. Then, by cooling the power semiconductor by refrigerant gasto be discharged, the problems in the conventional case using suckedrefrigerant gas will be solved at one sweep. Where, although asemiconductor using silicon carbide (SiC), gallium nitride (GaN) ordiamond, etc., is known as the wide band gap power semiconductor, anytype of wide band gap power semiconductor element can be used as long asit has such a high upper limit of the operating temperature as describedabove.

Further, since such a wide band gap power semiconductor element is smallin on-state resistance and small in switching loss, the heat generatedby the element itself is also small, and therefore the amount of heatrequired for cooling the element is small as compared with that for theSi power semiconductor element. From this point of view, it is possibleto cool the wide band gap power semiconductor element sufficiently andefficiently by cooling due to the refrigerant gas to be discharged.

Furthermore, because the wide band gap semiconductor element has a highheatproof temperature, it is not necessary to create an extra lowtemperature as a cooling source, and therefore, the total efficiencydetermined as the whole of the refrigeration circuit system is alsoimproved.

In the drive circuit-integrated electric compressor according to thepresent invention, it may be configured so that the power semiconductorelement of motor drive circuit is cooled by refrigerant gas to bedischarged, and various types of configurations can be employed asconcrete cooling structures. For example, a structure may be employedwherein the above-described power semiconductor element is mounted on ahigh heat-conduction circuit board and a back surface of the circuitboard is configured to be cooled by the refrigerant gas to be dischargedthrough a wall of the compressor (a wall inside the compressor). Byusing a circuit board comprising a high heat-conduction material, forexample, a material made of a high heat-conduction ceramic, etc., thepower semiconductor element is cooled through the circuit board with ahigh efficiency.

Further, in the drive circuit-integrated electric compressor accordingto the present invention, a structure may be employed wherein theabove-described power semiconductor element is coated with a lowheat-conduction resin. Furthermore, a structure may be employed whereina low heat-conduction heat shielding member is provided at a positionbetween the above-described power semiconductor element and otherelectronic parts. Because heat radiation to other electronic parts canbe prevented by being shielded by such a low heat-conduction resin or alow heat-conduction member, the temperature elevation of the otherelectronic parts can be suppressed, and the reliability as the whole ofthe motor drive circuit, and further, as the whole of the compressor, isimproved.

The kind of refrigerant used in the drive circuit-integrated electriccompressor according to the present invention is not particularlylimited. Not only conventional refrigerants used generally, but also CO₂and HFC1234yf can be used as the refrigerant. In the case of CO₂refrigerant, although the refrigerant is used under a higher-temperatureand higher-pressure condition, it is sufficiently applicable for coolingthe above-described wide band gap semiconductor element. Further,HFC1234yf, which is a new refrigerant announced recently, is alsosufficiently applicable for cooling the power semiconductor element.

In addition, in the drive circuit-integrated electric compressoraccording to the present invention, as the refrigerant gas to bedischarged for cooling the above-described power semiconductor elementin the drive circuit, for example, it is possible to use any ofrefrigerant gas to be discharged which has passed through a built-inmotor and a compression part (a compression mechanism part) in thisorder, refrigerant gas to be discharged which has passed through acompression part and a built-in motor in this order and refrigerant gasto be discharged which passes through a built-in motor part after havingpassed through a compression part (for example, as shown in theembodiment described later, refrigerant gas to be discharged whichpasses through a discharged gas path formed at a position between astator of a built-in motor and a drive circuit housing after havingpassed a compression part).

Further, the drive circuit-integrated electric compressor according tothe present invention is suitable, for example, for a scroll-typecompressor in particular. That is, in the case of a scroll-typecompressor, because a motor drive circuit can be easily disposed at aposition near a path for refrigerant gas to be discharged, it ispossible to cool the power semiconductor element of the motor drivecircuit efficiently.

Furthermore, the drive circuit-integrated electric compressor accordingto the present invention is particularly suitable as a compressormounted on a vehicle. A structure for efficiently cooling the powersemiconductor can be realized by a simple configuration substantiallywithout a gain of weight. In particular, this electric compressor issuitable particularly for a compressor installed in a refrigerationcircuit of an air conditioning systems for vehicles.

EFFECT ACCORDING TO THE INVENTION

In the drive circuit-integrated electric compressor according to thepresent invention, because refrigerant gas to be discharged is utilizedfor cooling the power semiconductor element, an elevation of the gastemperature before the compression and discharge of sucked refrigerantgas as in the conventional method may not be caused, a high compressionefficiency can be achieved and the coefficient of performance (COP) ofthe compressor can be improved. Particularly, in the case using a wideband gap power semiconductor element as a power semiconductor element,the power semiconductor element can be efficiently cooled by utilizingrefrigerant gas to be discharged.

Further, because the gas temperature is not elevated until suckedrefrigerant gas is compressed and discharged, it is possible to improvethe durability and life of the compressor. Furthermore, because suckedrefrigerant gas does not have to pass through a heat exchange route forcooling as in a conventional structure, it is also possible to reducethe pressure loss.

BRIEF EXPLANATION OF THE DRAWINGS

FIG. 1 is a schematic vertical sectional view of a drivecircuit-integrated electric compressor according to a first embodimentof the present invention.

FIG. 2 is a circuit diagram of a motor drive circuit and a controlcircuit in the compressor depicted in FIG. 1.

FIG. 3 is a schematic vertical sectional view of a drivecircuit-integrated electric compressor according to a second embodimentof the present invention.

FIG. 4 is a schematic vertical sectional view of a drivecircuit-integrated electric compressor according to a third embodimentof the present invention.

EMBODIMENTS FOR CARRYING OUT THE INVENTION

Hereinafter, desirable embodiments of the present invention will beexplained referring to figures.

FIG. 1 shows a drive circuit-integrated electric compressor 100according to a first embodiment of the present invention. In FIG. 1,symbol 1 indicates a drive circuit housing, symbol 2 indicates acompressor housing and symbol 3 indicates a suction housing. In thisembodiment, a motor 13 constituted by a stator 4, a rotor 5 and a motorcoil 6 is incorporated into suction housing 3. By this motor 13, a driveshaft 7 supported by a bearing 23 at a condition free to rotate isrotationally driven and a compression part 8 (a compression mechanismpart) is operated. Compression part 8 is configured, for example, as ascroll type.

In compressor 100, a refrigerant path depicted by arrows is formed. Therefrigerant gas is sucked at a suction port 9 formed in suction housing3, passes through a motor part, is compressed at compression part 8, andthen is discharged from a discharge port 10 formed in drive circuithousing 1 to an external circuit. Symbol 11 indicates a sealed terminalA and symbol 12 indicates a sealed terminal B, and they supply powerfrom a motor drive circuit 30 to motor 13, together with a lead wire 24.

Motor drive circuit 30 has a power semiconductor element 15, which isinstalled on a power circuit board 14. In this embodiment, a wide bandgap power semiconductor element is used as this power semiconductorelement 15. Power circuit board 14 is fixed to a wall 26 in drivecircuit housing 1, which is located at a position where refrigerant gasto be discharged passes, via insulation material 16, and by utilizingrefrigerant gas to be discharged which passes through a dischargechamber 25, power semiconductor element 15 mounted on power circuitboard 14 is cooled. In order to improve cooling efficiency, powercircuit board 14, further, insulation material 16, are made of a highheat-conduction ceramic, etc.

Symbol 17 indicates a board of control circuit for controlling motordrive circuit 30, and a micro controller 18 constituting the controlcircuit is installed on this control circuit board 17. Electric power issupplied from an external power source through a connector 22, andtherefrom, the power is supplied to motor drive circuit 30 through anoise filter 20 and a smoothing capacitor 19. These circuit parts arecovered with a lid 21, and shielded from the outside. Furthermore, inthis embodiment, a low heat-conduction insulation resin 27 is providedon power circuit board 14, and power semiconductor element 15 is coveredwith this resin 27 so that heat radiation from power semiconductorelement 15 to other electronic parts is prevented. Where, symbol 28 inFIG. 1 shows a bolt connecting the respective housings to each other.

Motor drive circuit 30 and its control circuit are configured, forexample, as shown in FIG. 2. In FIG. 2, motor drive circuit 30 isprovided in electric compressor 100 as described above, and by supplyingan output from motor drive circuit 30 to each of motor coils 6 of abuilt-in motor 13 through sealed terminal 11, motor 13 is rotationallydriven and the compression by compression part 8 is carried out.Electric power from an external power source 42 (for example, a battery)is supplied to this motor drive circuit 30, then is supplied to aninverter 41 through noise filter 20 containing a coil and a capacitorand through smoothing capacitor 19, and is supplied to motor 13 afterthe direct current from power source 42 is converted into a pseudothree-phase alternate current by inverter 41. Signals controlling thecompressor are supplied to motor control circuit 45 from, for example,an air conditioning unit for vehicles 44 through a connector for controlsignal 43. The above-described inverter 41 is provided with three setsof power semiconductor elements 15, 6 elements in total, each consistingof a Schottky barrier diode SiC-SBD 47 and a SiC-MOSFET 46 as wide bandgap semiconductor. Similar motor drive circuit and control circuit canbe used in the drive circuit-integrated electric compressors accordingto second and third embodiments described later.

In the embodiment thus constructed, power semiconductor element 15 iscooled efficiently as follows. As aforementioned, because the upperlimit of the operating temperature of a wide band gap powersemiconductor is 200° C. or more whereas the upper limit of theoperating temperature of a conventional Si power semiconductor isapproximately 150° C., without using sucked refrigerant gas, the wideband gap power semiconductor can be cooled sufficiently even by atemperature of refrigerant gas to be discharged which is generally in atemperature range of 100-150° C. Therefore, an elevation of thetemperature of the sucked refrigerant gas in the conventional coolingmethod can be prevented and the compression efficiency can be improved.Further, by suppressing the elevation of the temperature of the suckedrefrigerant gas, the life of respective portions in the compressor canbe improved. Furthermore, because it is not necessary to specially forma gas path for cooling a power semiconductor element by a suckedrefrigerant gas, the reduction of the pressure loss can also beachieved.

In addition, as aforementioned, because a wide band gap powersemiconductor is small in on-state resistance and small in switchingloss, a heat generated by the element itself is also small, andtherefore, the amount of heat for cooling may be smaller than that foran Si power semiconductor. Therefore, even refrigerant gas to bedischarged can cool the element sufficiently.

In addition, as shown in this embodiment, by covering powersemiconductor element 15 with low heat-conduction resin 27, for example,the heat radiation to electronic parts, smoothing capacitor 19 and noisefilter 20 which are mounted on control circuit board 17 can beeliminated so that the elevation of temperature can be prevented, andproper operation of these electronic parts can be ensured. In addition,although it is not depicted in figures, it is also effective topartition between power semiconductor element 15 and control circuitboard 17 by a heat shielding plate.

Further, in the structure of this embodiment, because it is notnecessary to consider a path of the sucked refrigerant gas and theposition of suction port 9 is not restricted, the design freedomincreases and the installation to a vehicle is facilitated.

Furthermore, as aforementioned, because the wide band gap semiconductorelement has a high heatproof temperature and it is not necessary tocreate an extra low temperature as a cooling source, the totalefficiency of the refrigeration circuit system is improved. Furthermore,in case where motor 13 has a rotor using a neodymium magnet, the magnetwould be demagnetized to some extent by the temperature elevation. Inthe conventional case where the power semiconductor element is cooled bythe sucked refrigerant gas, because the sucked refrigerant gas passesthrough a motor after the gas temperature has elevated due to the heatexchange, there has been a fear that the magnet may be demagnetized tosome extent, but in the case of this embodiment, this problem is to besolved.

FIG. 3 depicts a drive circuit-integrated electric compressor 200according to a second embodiment of the present invention. In thisembodiment, the refrigerant gas sucked from suction port 9 is introduceddirectly into compression part 8 through suction gas chamber 31, passesthrough motor 13, cools power semiconductor element 15 and then isdischarged from discharge port 10. Because a magnet of motor 13 isexposed to refrigerant gas to be discharged, it is preferred to use nota neodymium magnet having a demagnetization characteristic at hightemperature, but a ferrite magnet, etc. having a demagnetizationcharacteristic at low temperature. Further, it is also preferred to usea motor which has no fear of demagnetization (an induction motor, aswitched reluctance motor, etc.). The other configurations of thisembodiment are in accordance with those of the aforementioned firstembodiment.

In such a configuration, the sucked refrigerant gas is not heatedbecause the gas enters directly into compression part 8 before passingthrough motor 13. Therefore, it is possible to further improve thecompression efficiency. Further, because the sucked refrigerant gasenters directly into compression part 8 without passing through motor13, the pressure loss therebetween does not substantially occur.

FIG. 4 depicts a drive circuit-integrated electric compressor accordingto a third embodiment of the present invention. In this embodiment, adrive circuit is mounted in the radial direction of motor 13. The suckedrefrigerant gas coming out of compression part 8 passes throughdischarge gas path 33 formed between stator 4 of motor 13 and drivecircuit housing 32, and cools power semiconductor element 15 of themotor drive circuit. A drive circuit is incorporated into drive circuithousing 32, and motor 13 is incorporated into drive circuit housing 32.Compression part 8 is incorporated into suction housing 3. The suckedrefrigerant gas enters into suction gas chamber 31 and then is sent tocompression part 8. The other configurations of this embodiment are inaccordance with those of the aforementioned first embodiment.

In such a configuration, while an excellent cooling effect of powersemiconductor element 15 is obtained, the length of electric compressor300 in the axial direction is shortened and the automotive installationfacility is improved.

FIG. 1, FIG. 3 and FIG. 4 show configurations that power semiconductorelement is mounted on a high heat-conduction circuit board. However,though it is not depicted in figures, it goes without saying that thesame effect can be achieved when a discrete-type wide band gap powersemiconductor element is mounted directly on a wall of a compressor.

INDUSTRIAL APPLICATIONS OF THE INVENTION

The structure of the drive circuit-integrated electric compressoraccording to the present invention can be applied to any type electriccompressor assembled with a power semiconductor element, andspecifically, is suitable for a compressor mounted on a vehicle, and inparticular, is suitable for a compressor for air conditioning system forvehicles.

EXPLANATION OF SYMBOLS

-   1: drive circuit housing-   2: compression part housing-   3: suction housing-   4: stator-   5: rotor-   6: motor coil-   7: drive shaft-   8: compression part-   9: suction port-   10: discharge port-   11, 12: sealed terminal-   13: motor-   14: power circuit board-   15: power semiconductor element-   16: insulation material-   17: control circuit board-   18: microcontroller-   19: smoothing capacitor-   20: noise filter-   21: lid-   22: connector-   23: bearing-   24: lead wire-   25: discharge chamber-   26: wall-   27: resin-   28: bolt-   30: motor drive circuit-   31: suction gas chamber-   32: drive circuit housing-   33: discharge gas path-   41: inverter-   42: external power source-   43: connector for control signals-   44: air conditioning control unit-   45: motor control circuit-   46: SiC-MOSFET-   47: SiC-SBD-   100, 200, 300: drive circuit-integrated electric compressor

1. A drive circuit-integrated electric compressor into which a motordrive circuit having a power semiconductor element is incorporatedintegrally, wherein said electric compressor is configured so that saidpower semiconductor element in said drive circuit is cooled byrefrigerant gas to be discharged.
 2. The drive circuit-integratedelectric compressor according to claim 1, wherein said powersemiconductor element is a wide band gap semiconductor element.
 3. Thedrive circuit-integrated electric compressor according to claim 1,wherein said power semiconductor element is mounted on a highheat-conduction circuit board and a back surface of said circuit boardis configured to be cooled by refrigerant gas to be discharged through awall of said compressor.
 4. The drive circuit-integrated electriccompressor according to claim 1, wherein said power semiconductorelement is coated with a low heat-conduction resin.
 5. The drivecircuit-integrated electric compressor according to claim 1, wherein alow heat-conduction heat-shielding member is placed at a positionbetween said power semiconductor element and other electronic parts. 6.The drive circuit-integrated electric compressor according to claim 1,wherein CO₂ is used as refrigerant.
 7. The drive circuit-integratedelectric compressor according to claim 1, wherein HFC1234yf is used asrefrigerant.
 8. The drive circuit-integrated electric compressoraccording to claim 1, wherein said refrigerant gas to be discharged forcooling said power semiconductor element in said drive circuit isrefrigerant gas to be discharged which has passed through a built-inmotor and a compression part in this order.
 9. The drivecircuit-integrated electric compressor according to claim 1, whereinsaid refrigerant gas to be discharged for cooling said powersemiconductor element in said drive circuit is refrigerant gas to bedischarged which has passed through a compression part and a built-inmotor in this order.
 10. The drive circuit-integrated electriccompressor according to claim 1, wherein said refrigerant gas to bedischarged for cooling said power semiconductor element in said drivecircuit is refrigerant gas to be discharged which passes through abuilt-in motor part after having passed through a compression part. 11.The drive circuit-integrated electric compressor according to claim 1,wherein said electric compressor is a scroll-type compressor.
 12. Thedrive circuit-integrated electric compressor according to claim 1,wherein said electric compressor is a compressor mounted on a vehicle.13. The drive circuit-integrated electric compressor according to claim1, wherein said electric compressor is a compressor installed in arefrigeration circuit of an air conditioning system for vehicles.